Jim
I also was looking at the Cumberland to do this Fall. I read Jerry Hay's various posts with his boats (and other books), as well as the Cumberland River Guide book. My impression was that there were going to be some fairly good fluctuations of water depth as water was let out of Wolfe Dam. Also seemed to be a number obstructions.
Our experience is that there are two ways to have "least" daft on the 22's and 25's--one is to run at a good plane, which will reduce the draft maybe 3- 6 inches more than the distance from the ventilation plate on the motor (about even with the boat bottom--so maybe 18" plus 3" on the 22. A bit more on the 25. or I can get the boat over a sand bar at our entrance, with a little over 18" of water... with the engine trimmed up to the "trailer position", but with the water intake still picking up water (and the engine peeing). For example in some side branches of the St. John's with mud bottom, recently boats could not make it thru an area, at displacement speed, but drew less on a plane and could get thru...
There is no way you are gong to run in the Cumberland at that area, on a plane, not knowing what is down there....Our decision is to not attempt that part of the Cumberland. What a jon boat can get over, and a C Dory 25 are quite different.